Electric discharge tube



Feb. 2 1935. A. SALOMON 1,992,888

ELECTRIC DISCHARGE TUBE Filed Oct. 17, 1932 Patented Feb. 26, 1935PATENT. OFFICE 1,992,888 7 ELECTRIC DISCHARGE TUBE Adolf Salomon,Berlin-Charlottenburg, Germany, .assignor to Carl LindstriimAktiengesellschaft,

Berlin, Germany Application October 17, 1932, Serial In Germany October20, 193 1 (01. cam-27.5)

Claims.

This invention relates to a gas-filled electric discharge valve foramplification purposes which can be used, for example, in radioapparatus,

sound film installations, devices-for electrical re- 5 cording andreproduction of disc records and in general for amplifying signals andelectrical oscillations.

The object of the invention is toproduce an amplifying valve which, ascompared with known evacuated and gas-filled amplifying valves has astraight line amplifying action which gives many times the amplificationof the known valves. A further object is to provide an amplifying valvewhich makes it directly possible to obtain a degree of amplificationwhich is only possible with known valves by means of several valvesconnected in series so that the amplification of. a single valve is suchthat, for example, without interposing further relays or amplifiers theoutput energy of the valve can be used directly for driving a dynamicloud speaker system. 7

It has now been found that the known cathode dark space in combinationwith a valve containing a rare gas in which the pressure is kept verylow can be utilized to give amplification factors which cover a veryhigh range of frequencies withv practically straight line amplification.The amplifying valves constructed according to the invention do not givethe distortion which occurs with the ordinary valves on account'of thespace charge efiects. This is due to the fact that the parts betweenthecathode andthe anode consisting of a dark space and an ionized parttransmit such energy potentials that space charges if they are presentoutside the above-mentioned space have no effect or a negligible effecton the static discharge path. 1

According to the invention the arrangement is made such that in thedischarge tube a Crookes dark space extends between the cathode and thecontrol grid while the space between the control grid and the anode iscompletely filled by a (luminous) glow discharge.

The discharge tube according to the invention is provided with an anode,one or more grids and'a cathode and has a filling consisting of a raregas or a mixture of rare gases.

Helium has been found very satisfactory for the filling gas and ispreferably used under a pressure oil-5 mm. of mercury.

In one constructional form of the invention the discharge tube has acold cathode which is preferably coated with an alkali metal. Thecathode is surrounded by a grid of fine mesh wire fabric or wire woundin a helix While an anode of metal sheet encloses the whole. It can beoperated with voltages of from 100-300 volts.

In a further form of the invention an incandescentcathode which may, forexample, be an indirectly heated oxide cathode (Wehnelt cath- 5 ode), issurrounded by a cylindrical grid of wire wound in a'helix which again isenclosed 'by a cylindrical anode of sheet 'metal. The whole electrodestructure is supported on a pinch in a known manner by means ofsupporting wires which alsopartly serve as lead-inwires. The valve canfurther be formed in the usual manner or a substance may be deposited onthe glass bulb of the valve in order, for example, to bind the gasresidue released from the oxide cathodeand the other electrodes duringoperation and to prevent adulteration of the rare gas filling whichwould readily cause unstable conditions in operation.

The discharge tube according to the invention can be operatedin asimilar manner to the known amplifying valves. The grid voltage may havepractically any desired value. Very. good results have been obtainedwith alternating voltages of 2-4 volts While anode voltages of 150-200volts were used.

The discharge valves according to the invention, as compared with knownhigh vacuum valves; have much steeper characteristics and theamplification factors are many times those of high vacuum valves. Thus,for example, it is possible to obtain an amplification of 120- 150 whilethe length of life is sufiicient and it is practically completely stablein operation. With suitable constructionof the discharge tube, however,amplifications of up to 500 times may be obtained. This is probably dueto the complete absence of space charges in the space between thecontrol grid and the anode on account of the presence oi. the rare gaswhich is to a large extent ionized during operation.

A constructional example of the invention is 4 illustrated in theaccompanyingdrawing.

The discharge tube shown in the drawing has a glass bulb 1 to which isfused a pinch 2. 0n the pinch, by means of a supporting wire 3 and acarrying wire 4, an incandescent cathode'5 is 7 arranged which may be anindirectly heated oxide cathode. The supporting wires 3 and 4 are alsoemployed for leading in the heating current and are connected with theleading in wires fused into the pinch 2. The incandescent cathode 5 issurrounded by a cylindrical grid 6 which consists of a wire wound in ahelix and is carried by a supporting wire 7 which is also employed asleading in wire. Around the grid is arranged a cylinl0 s V as usual, isonly a few volts.

drical anode 8 which is carried by supporting Wires arranged on thepinch, of which one supporting wire 9 is connected with the lead in wirefor the anode which passes through the pinch 2. The discharge tube isprovided with a gettering material, for example vaporized magnesium orbarium, which may cover a part of the glass bulb. The gas fillingpreferablyconsists of helium at a pressure of 1-5 mm. of mercury. Theanode voltage may be from 1004500 volts while the heating voltage, Withsuch a valve the conditions to be obtained according to the inventioncan be maintained because a Crookes dark space is formed between thecathode 5 and the grid 6 and the space between the grid 6 and the anode8 is completely filled by, a luminous glow discharge' The position ofthe grid must be such that the space between the cathode and the grid isentirely filled by Crookes dark zone.

The zone must not extend beyond the grid. That Crookes dark spacebetween the cathode and anode and so spaced from the cathode that during operation Crookes dark zone extends between the cathode and thecontrol grid and is confined tween the-cathode and anode.

3. A gas filled discharge tube as claimed in claim Lin which the anodeis tubular, the cathode extends through thecenter ofthe anode and thegrid is helical and extends around the cathode and is spaced therefromand from the grid, so that the Crookes dark space is between the cathodeand the grid and the luminous glow discharge is between the grid and theanode.

i. A gas filled discharge tube as claimed in claim 1 in Whichthepressure of the gas filling is from i. to 5mm, of mercury, having ananode, a cathode and a grid arranged in the Crookes dark space betweenthe cathode and anode.

5. A gas filled discharge tube as claimed in claim 1 in which the gasfilling consists of helium, having an anode, a cathode and a gridarranged in the Crookes dark space between the cathode and anode.

ADOLF SALOMON.

